4th axis and G1 moves

I've had a movement demo script for my delta for a while now. Since I've changed my machine to have a 4th axis, carrying the extruder, the script broke. The problem lies with the G1 move, DWC console reports that the target position is not reachable. I suspect the issue is that no U parameter is specified to move to. I however would find it weird if I would have to specify U, since it is not trivial to calculate by hand.
G28 ; Home G1 X100 Y0 Z600 F750 ; Move to starting position M300 S3000 P1000 ; Play a 1s beep G4 P1000 ; Wait a second G2 X100 Y0 Z5 I100 J0 F750 ; Helical move down M300 S3000 P1000 ; Play a 1s beep G4 P500 ; Wait 500ms G3 X100 Y0 Z600 I100 J0 F750 ; Helical move up

First, are you running firmware 2.04RC1? It fixes a coupe of bugs in 2.03 that affected delta printers.
You do not have to give a U coordinate if you have set up U as a 4th tower as described on the wiki. However, if you have chosen an unsuitable combination of the 4th "rod" length (aka effective Bowden tube length) and the XY coordinates of the 4th tower (aka extruder outlet), then this may of course restrict the movement. To give a trivial example, suppose the 4th tower XY coordinates are X0 Y0 and the length is 100mm; then anything at a radius from the centre greater than 100mm would be unreachable.
What coordinates and rod length did you specify for the 4th tower? Please post your config.g file.

I should note that moving with the buttons on the DWC dashboard work just fine. So I would say there is no issue with 'reachability'.
Here's my config.g; Configuration file for Deltex ; ===================== GENERAL SETTINGS ===================== M111 S0 ; Debug off M550 PDeltex ; Machine name and Netbios name M555 P2 ; Repetier Output M575 P1 B57600 S1 ; PanelDue Comm Setup M540 P0xBE:0xEF:0xDE:0xAD:0xFE:0xEA ; MAC Address M552 S1 ; Enable WiFi M586 P1 S0 ; Disable FTP M586 P2 S0 ; Disable Telnet ; ===================== MOVEMENT SETTINGS ==================== G21 ; Set Units to Millimeters G90 ; Set to Absolute Positioning M83 ; Set extruder to relative mode M584 X0 Y1 Z2 U4 E3 ; Assign drives to each motor M569 P0 S0 ; Drive 0 (X) goes backwards M569 P1 S0 ; Drive 1 (Y) goes backwards M569 P2 S0 ; Drive 2 (Z) goes backwards M569 P3 S0 ; Drive 3 (E) goes backwards M569 P4 S1 ; Drive 4 (4th) goes backwards M574 X2 Y2 Z2 U2 S1 ; Endstop configuration (all endstops at high end, active high) M665 L500.000:500.000:500.000:224.000 R239.410 H604.996 B130.0 X0.050 Y0.762 Z0.000 ; Diagonal rod length, delta radius, printable radius and homed height M669 K3 X0 Y0 ; Location of the 4th axis tower M666 X1.697 Y2.831 Z4.528 A0.00 B0.00 ; Endstop adjustments M350 X16 Y16 Z16 E16 U16 I1 ; Set 16x microstepping with interpolation M92 X200 Y200 Z200 U80 E414 ; Set steps/mm M906 X2100 Y2100 Z2100 U600 E700 I45 ; Set motor currents (mA) and increase idle current to 45% M201 X2000 Y2000 Z2000 U2000 E5000 ; Accelerations (mm/s^2) M203 X10000 Y10000 Z10000 U10000 E20000 ; Maximum speeds (mm/min) M566 X400 Y400 Z400 U400 E2000 P1 ; Maximum instant speed changes (mm/min) ; ================ HEATING AND COOLING SETTINGS ============== ; Thermistors ;M305 P0 B4725 C7.060000e8 ; Bed temperature sensor parameters M305 P0 B3950 ; Bed temperature sensor parameters M305 P1 B4725 C7.060000e8 ; Hotend temperature sensor parameters M570 S180 ; Configure heater fault detection, allow it 180 seconds M307 H0 A633.5 C317.1 D3.7 S1.00 V24.2 B0 F10 ; Set bed heating process parameters and use PID at 10Hz M307 H1 A520.7 C251.5 D5.2 S1.00 V24.2 B0 ; Set hotend heating process parameters and use PID M143 H0 S200 ; Set maximum bed temperature to 200 ; Fans M106 P0 H1 ; disable thermostatic mode for fan 0 (part cooling) M106 P1 S255 T45 H1 ; enable thermostatic mode for fan 1 (hotend) ;M106 P2 T35:65 H100:101:102 ; enable thermostatic mode for fan 2 (system) ; ====================== TOOL SETTINGS ======================= M563 P0 D0 H1 S"Hotend" ; Define hotend G10 P0 S0 R0 ; Set tool 0 operating and standby temperatures M207 S0 R0 F3000 T1200 Z0 ; Set default retraction settings ; =================== CALIBRATION SETTINGS =================== M558 P5 A5 S0.03 X0 Y0 Z0 H2 F250 T10000 ; Z probe is a switch, tap max 5 times with 0.03 mm tolerance, move 2mm above the bed at 250 mm/min and travel at 10000 mm/min G31 X0 Y0 Z0.23 P10 ; Set the zprobe height and threshold (more negative values translate into a higher nozzle) M557 R120 S15 ; Define probing mesh grid M912 P0 S12.35 ; Set temperature offset for MCU T0 ; Select hot end M501 ; Load settings from configoverride.g
And configoverride.g
; configoverride.g file generated in response to M500 at 20190724 19:54 ; This is a systemgenerated file  do not edit ; Delta parameters M665 L500.000:500.000:500.000:224.000 R239.107 H610.217 B130.0 X0.079 Y0.315 Z0.000 M666 X1.913 Y3.081 Z4.994 A0.12 B0.23 ; Heater model parameters M307 H0 A546.0 C223.9 D4.4 S1.00 V24.2 B0 M307 H1 A520.7 C251.5 D5.2 S1.00 V24.2 B0 M307 H2 A340.0 C140.0 D5.5 S1.00 V0.0 B0 M307 H3 A340.0 C140.0 D5.5 S1.00 V0.0 B0 M307 H4 A340.0 C140.0 D5.5 S1.00 V0.0 B0 M307 H5 A340.0 C140.0 D5.5 S1.00 V0.0 B0 M307 H6 A340.0 C140.0 D5.5 S1.00 V0.0 B0 M307 H7 A340.0 C140.0 D5.5 S1.00 V0.0 B0 G10 L2 P1 X0.00 Y0.00 Z0.00 U0.00 G10 L2 P2 X0.00 Y0.00 Z0.00 U0.00 G10 L2 P3 X0.00 Y0.00 Z0.00 U0.00 G10 L2 P4 X0.00 Y0.00 Z0.00 U0.00 G10 L2 P5 X0.00 Y0.00 Z0.00 U0.00 G10 L2 P6 X0.00 Y0.00 Z0.00 U0.00 G10 L2 P7 X0.00 Y0.00 Z0.00 U0.00 G10 L2 P8 X0.00 Y0.00 Z0.00 U0.00 G10 L2 P9 X0.00 Y0.00 Z0.00 U0.00

Those look OK to me. Can you experiment with sending various G1 commands, to see what does/doesn't work? Does it depend on the Z coordinate, or only on X and Y?

@dc42 Below are the moves I tried and in the process I've figured out what the problem was. RRF is behaving as it should: X100 is well within the limits and so is Z600, but not X100 Z600 at the same time.